Do all Ontario professional corporations need the words 'Professional Corporation' in their name?

Yes, as a general rule. Ontario's professional-corporation regime requires the corporation's legal name to include the words "Professional Corporation," or the French equivalent, so that anyone dealing with the corporation can identify it as a regulated professional entity rather than an ordinary business corporation. This naming requirement applies on top of the standard corporate-naming rules that apply to any Ontario corporation, such as clearing a name search.

Beyond the required "Professional Corporation" designation, most governing bodies layer on their own additional naming requirements — for example, requiring the name to include a shareholder's surname or the profession itself, and restricting certain descriptive or promotional wording. These profession-specific rules are enforced separately by the regulator when it reviews the corporation for its certificate of authorization, so a name that's accepted by the corporate registry can still be rejected by the governing body. Before finalizing a name, confirm both the general corporate-naming rules and your specific governing body's naming bylaws, since getting this wrong can delay both the incorporation and the certificate application.